Pluto dwarfed by Eris

Eris and Pluto relative to the Moon

Strife in the Kuiper Belt

It's 14 years ago today that astronomers at Palomar Observatory in San Diego, California, discovered the dwarf planet Eris in the outreaches of the Kuiper Belt.

The discovery by Mike Brown, Chad Trujillo and David Rabinowitz resulted from images taken on 21 October 2003 and was announced almost two years later on 29 July 2005.

Named after the Greek goddess of discord and strife, Eris' discovery rattled the general model of our solar system... the detection of the icy dwarf planet provoking huge debate about Pluto's classification as a planet.

Since Eris appeared to be slightly larger than Pluto it begged the question that if Pluto qualified as a full-fledged planet, then so should it. Astronomers attending the International Astronomical Union meeting in 2006 worked to settle this dilemma and Pluto was reclassified as a dwarf planet along with Eris and the asteroid Ceres, the most massive member of the asteroid belt that lies between the orbits of Mars and Jupiter.

More recent images from NASA's New Horizons probe have in fact showed that Pluto is bigger than originally thought at 2,370km across and is actually probably slightly larger than Eris, although it is difficult to distinguish which of the two is the largest object in the disc-like zone beyond the orbit of Neptune called the Kuiper Belt.

This distant realm is populated with thousands of miniature icy worlds, which formed early in the history of our solar system about 4.5 billion years ago. These icy, rocky bodies are called Kuiper Belt objects, transneptunian objects, or plutoids.

Eris is believed to take about 557 Earth years to make one trip around the sun and is the most distant object ever seen in orbit around it, even more distant than Sedna, the Kuiper Belt object discovered in 2003. It is almost 10 billion miles from the sun and more than three times more distant than Pluto and takes more than twice as long to orbit the sun as Pluto.

With a radius of about 722 miles, Eris is about a fifth of the Earth's radius and, like Pluto, is a little smaller than our moon.

Eris most likely has a rocky surface similar to Pluto. Scientists believe surface temperatures vary from about -217 to -243 degrees Celsius and it is often so far from the sun that its atmosphere collapses and freezes, falling to the surface as snow.

Eris has a very small moon called Dysnomia, which has a nearly circular orbit lasting about 16 days. This moon is named after Eris' daughter, the demon goddess of lawlessness.

As Eris orbits the sun it completes one rotation every 25.9 hours, making days on the dwarf planet similar in length to those on Earth.

For more information visit the NASA website.